Optical investigations on $Y_{2-x} Bi_x Ru_2 O_7$: Electronic structure evolutions related to the metal-insulator transition

TL;DR

This study investigates optical conductivity in Y_{2-x}Bi_xRu_2O_7 compounds, revealing spectral changes near the metal-insulator transition that suggest doping effects from Bi cations influence electronic structure.

Contribution

It provides new insights into the electronic structure evolution across the MIT in pyrochlore ruthenates, highlighting the role of filling-controlled mechanisms and Bi doping effects.

Findings

Spectral changes occur around x=0.8 indicating MIT

Suppression of correlation-induced peak with increasing x

Shift of p-d charge transfer peak to lower energies

Abstract

Optical conductivity spectra of cubic pyrochlore $Y_{2-x} Bi_x Ru_2 O_7$ (0.0$\leq ${\it x}$\leq $2.0) compounds are investigated. As a metal-insulator transition (MIT) occurs around {\it x}$=$0.8, large spectral changes are observed. With increase of {\it x}, the correlation-induced peak between the lower and the upper Hubbard bands seems to be suppressed, and a strong mid-infrared feature is observed. In addition, the $p-d$ charge transfer peak shifts to the lower energies. The spectral changes cannot be explained by electronic structural evolutions in the simple bandwidth-controlled MIT picture, but are consistent with those in the filling-controlled MIT picture. In addition, they are also similar to the spectral changes of Y$_{2-x}$Ca$_{x}$Ru$_{2}$O$_{7}$ compounds, which is a typical filling-controlled system. This work suggests that, near the MIT, the Ru bands could be doped with the easily polarizable Bi cations.